I would say a 11.75 would probably be a better fit for a player who is 6'4 with large hands. One thing you didn't bring up is what kind of budget you have to spend. I would buy the A2000 $200 before the A2K $350, my SS has had both and he doesn't see that much of a difference in them for the $150 upgrade. Marucci also makes several really good gloves. And of course the 2 Rawlings mentioned are really good gloves, but can be pricey. I would definitely recommend he go to a Dicks or glove store and try some on to see what he likes. He also could ask to try out some of his teammates gloves.